staging: r8188eu/core: remove the check for NULL pointer in _rtw_enqueue_cmd()

Remove the check for _rtw_enqueue_cmd(), because
rtw_enqueue_cmd() already has a check of NULL pointer,
so this condition is not possible.

Signed-off-by: Qiang Ma <maqianga@uniontech.com>
Link: https://lore.kernel.org/r/20210616125332.31674-1-maqianga@uniontech.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>